1. Field of the Invention
The present invention relates to a novel amide- or imide-introduced copolymer useful as a photoresist resin in a lithography process using a light source suitable for forming a fine pattern of a highly integrated semiconductor device, a method for preparing the same, and a photoresist comprising the same.
2. Description of the Prior Art
To achieve high sensitivity in a microlithography for fabricating a semiconductor device, deep ultra violet (DUV) photoresist, a chemical amplification resist, has been the most extensively used recent times. Its composition comprises a photoacid generator and a matrix polymer reacting sensitively to acid.
Ideal photoresist is to satisfy such requirements as transparency to ArF light source, etch resistance, developability in 2.38% tetramethyl ammonium hydroxide (TMAH) and adhesiveness. However, it is very difficult to synthesize a photoresist resin superior in all of the requirements.
For example, a resin having a polyacrylate as a main chain is easy to synthesize but problematic in etch resistance and development. The etch resistance can be increased by introducing aliphatic ring moieties into the main chain.
Although the main chain is of polyacrylate type, with or without on aliphatic ring, problems still remain. The basic principle in the development of the photoresist film used for forming fine patterns of a semiconductor device resides in the formation of carboxylic acid by the photoacid generator. Because carboxylic acid is better dissolved in 2.38% TMAH than in hydroxy phenol, a solution used for KrF, the thereby produced pattern has a significant problem in that it has a round rather than a rectangular upper portion.
In addition, to overcome the phenomenon that an ArF light source alters the properties of the lens material, a pattern must be formed at a low level of energy because of the high sensitivity to light. To this end, either the amount of the photoacid generator in the photoresist composition or the carboxylic acid content of the photoresist resin must be increased.
Designed as it has been, the prior art solves to both of the above problems be cause the patterns have a round rather than a rectangular upper portion, making it virtually impossible to obtain a pattern of high resolution.